1. Field of the Invention
The present invention relates to a device for applying a magnetic field on a magneto-optical recording medium which allows information to be recorded, reproduced or deleted on itself, and to a magneto-optical head having the above magnetic head. More particularly, the invention relates to a floating type magnetic head which allows information to be rapidly overwritten on the magneto-optical recording medium in a magnetic field modulation system.
2. Description of the Related Art
A magneto-optical disk often referred to as a magneto-optical recording medium has become well known and used in the field of optical memories, because it has an advantage of rewritability. It has been under study for improving the practical performance of its rewritability operation. Today, it is required to develop a technique of improving the transfer speed of information in order to improve magnetic memories which are currently widely used. For meeting the requirement, current study and development have been focused on an overwriting technique.
A magnetic field modulation system is noted as one of the recording systems which allows an information signal to be rapidly overwritten on a magneto-optical memory. For such magnetic field modulation systems, the most suitable magnetic head for magneto-optical recording is a floating type magnetic head which includes a slider portion and a head core portion and is supported so as to be out of contact with the magneto-optical disk. This floating type magnetic head can quite rapidly invert the magnetic field applied to the magneto-optical recording medium.
As schematically shown in FIG. 1, the normal magneto-optical recording mechanism employing a magnetic field modulation system includes a magnetic head 22 and an optical head 23 integrally configured with each other. The magnetic head 22 is positioned opposite to the optical head 23 so that a magneto-optical disk 21 is inserted therebetween. The disk 21 is one example of a magneto-optical recording medium and rotates about a center axis M. As shown in FIG. 2, the magnetic head 22 is made of a slider 22a and a hook-like square head core 22b extending from one end of the slider 22a. The head core 22b is provided with a coil 22c wound on the outer peripheral surface thereof. As shown in FIG. 3, the bottom section 22d of the head core 22b is located so as to be parallel to the magneto-optical disk 21 and is formed as a square having the dimension of 0.2 mm.times.0.2 mm, for example.
This description will now be directed to the principle of how an information signal is rapidly overwritten on the disk in the magnetic field modulation system. As shown in FIG. 1, a laser beam 25 is focused through an objective lens 27 located at the optical head 23. The resulting laser beam 25 is continuously radiated on to a recording layer 24 contained on the magneto-optical disk 21 so as to heat the radiated spot on the recording layer 24 to about the Curie temperature at which the magnetic inversion is made possible. Next, while a magnetic field generated by the magnetic head 22 is rapidly inverted to correspond to an information signal, the magnetic head 22 and the optical head 23 integrally configured with each other are allowed to move in the radial direction of the magneto-optical disk 21, that is, in a direction orthogonal of the tracks contained on the disk 21. This results in magnetizing the heated spot of the recording layer 24 in the direction of the applied magnetic field 26, thereby allowing an information signal to be rapidly overwritten on the disk 21.
Each track pitch (not shown) formed on the magneto-optical disk 21 is as small as about 1.6 .mu.m. However, an actuator (not shown) provided at the optical head 23 allows the objective lens 27 to radially move on the magneto-optical disk 21 for the purpose of adjusting the position G of a focal point of the laser beam 25. With this fine adjustment, a radial recording bit is precisely positioned on the disk 21. The actuator moves the position G of the focal point of the laser beam 25 in the radial direction of the disk 21. The allowable movement is about .+-.100 .mu.m. The movement requires a magnetic field 26 generated by the magnetic head 22 to have such a large and wide magnetic field as to cover the overall moving range of the position G. In actuality, however, the head core 22b of the magnetic head 22 provides a small area 22d located in parallel to the disk 21, which means that it has a very small area 22d over which a vertically effective magnetic field is applied to the disk 21. In order to suppress the self-inductance of the magnetic head 22 to a smaller value, it is necessary to reduce the area of the head core 22b which area is proportional to the self-inductance.
As shown in FIGS. 2 and 3, the area 22d of the head core 22b is formed to give such a narrow magnetic field as disabling for covering the overall moving range of the laser beam 25. Such structure results in mismatching the magnetic field 26 generated by the magnetic head 22 from its correspondence with the position G of the focal point of the laser beam 25 and preventing an information signal from being overwritten on the mismatched portion, thereby producing a disadvantage in using such a structure for that purpose.